[unreadable] The primary objective of this SBIR program is to develop a novel 3D image guided adaptive therapy (3D IGAT) technique to improve the precision of radiation delivery during the course of Partial Breast Irradiation (PBI) treatment. We propose to perform patient repositioning and error correction based on accurate registration between the pre-operative CT scan and the 3D surface profiles of patient's breast acquired during the treatment. The 3D breast surface model will be acquired by a 3D surface imaging system to be designed and prototyped under this SBIR project. We will develop a deformable biomechanical finite-element breast model that establishes correlation between the 3D surface images and CT scans to derive the subsurface tumor location. Computational methods will be developed to estimate the true delivered dose given variations in patient geometry and to adaptively adjust he treatment plan when the delivered dose differs significantly from the planned dose with the aid of the finite element breast model. [unreadable] [unreadable]